In the near term and beyond, integrated optoelectronic devices will greatly increase the operating speeds and data transfer capabilities of present computing and communication systems. The present invention involves optical communication systems that use wavelength division multiplexing (WDM). This technology allows a telecommunication network to support multiple simultaneous users by partitioning a fiber's large bandwidth into a finite number of channels. Thus, the traffic generated by several users (S.sub.1,S.sub.2, . . . S.sub.N) is superimposed in a parallel form in one optical fiber, using a set of wavelengths (.lambda..sub.1,.lambda..sub.2, . . . , .lambda..sub.N). The design of the WDM systems are conditioned by the availability of suitable sources, multiplexers and demultiplexers. The present invention describes a WDM diode laser structure for generating light signals of discrete wavelengths using a monolithic structured device.
Prior art optical WDM methods include angular dispersion, optical filters and optical absorbers. The present invention uses the angular dispersion technique and in particular uses the geometric properties of a Rowland Circle type diffraction grating to achieve multi-channel WDM.
The closest known prior art that use the Rowland circle geometry for WDM dispersion of optical signals are contained in "Planar Rowland Spectrometer for Fiber-Optic Wavelength Demultiplexing" by Yen et al. published in Optics Letters, Vol. 6, No. 12 pp. 639-641 (1981) and "Monolithic InP/InGaAsP/InP Grating Spectrometer for the 1.48-1.56 um Wavelength Range" by Soole et al. published in Applied Physics Letters, Vol. 58, No. 18, pp. 1949-51, (1991). These articles teach the basic concept of using the Rowland gratings for spectrometer applications, but neither reference disclose or suggest an integrated array of laser source arrangement with grating in a monolithic construction for signal generation/amplification applications.
There are a number of WDM devices which are, however, different from the instant invention. These include Hunsperger et al.'s U.S. Pat. No. 4,773,063 optical WDM system that use a Bragg grating with a wavelength tuning means by use of an electro-optic grating within a planar waveguide configuration. Another device is Mahapatra et al.'s U.S. Pat. No. 4,715,027 which shows a WDM device of monolithic construction with an echelon grating. Neither of these inventions teach or suggest the instant invention's use of the Rowland gratings special diffraction properties or use a common directed array of diode lasers for an input signal/amplifier means within a monolithic construction.
Other teachings that show a multiple array of solid state laser device within a common monolithic construction include Hara et al.'s U.S. Pat. No. 4,971,415 which discloses a multi-beam laser emitting device with waveguide portion that is used for a light source in a plural beam scanning apparatus for recording purposes. However, this teaching does not disclose or suggest the use of a Rowland grating device as part of its monolithic construction wherein the grating forms part of the wavelength-feedback extended cavity.